1. Field of the Invention
The present invention relates to a gantry-type XY stage for use in an apparatus which performs local processing on a plane structure, and more particularly, to a gantry-type XY stage for use in a laser repair apparatus for liquid crystal displays, a laser repair apparatus for liquid crystal masks, a patterning apparatus for solar cell panels, a defect inspection apparatus for liquid crystal displays, a defect inspection apparatus for semiconductor devices, and the like.
2. Description of the Related Art
A laser repair apparatus for correcting manufacturing defects on a TFT (Thin Film Transistor) substrate of a liquid crystal display is provided with a gantry-type XY stage as a main component unit. The gantry-type XY stage is comprised of a base section which is a stationary portion, and a gantry section which is a movable portion disposed on the base section. The base section is provided with a granite plate, the top of which is an even stage surface. Also, the gantry section is provided with a pair of posts disposed on the granite plate for movements in a direction (Y-direction), and a beam (ridgepole) extended between top ends of the pair of posts. Then, a laser optical unit is mounted on the beam for movements in a direction (X-direction) orthogonal to the direction (Y-direction). Such a technology is disclosed in the home page of Sigma Co., Ltd. (http://www.sigma-fa.co.jp/2—3.html)[searched on Jul. 28, 2004], and in the home page of Sumitomo Heavy Industries, Ltd. (http://www.shi.co.jp/stage/prellys/20030318.htm) [searched on Jul. 28, 2004].
With such a structure, a liquid crystal display to be repaired is carried on the granite plate of the base section, the gantry section moves the laser optical unit to position this unit immediately above a defective portion of the liquid crystal display, such that the laser optical unit can irradiate the defective portion with laser light to repair the defective portion.
The gantry-type XY stage for use in such a laser repair apparatus for liquid crystal displays and the like is required to provide an extremely high shape accuracy with errors within approximately 10 μm. For this reason, the granite plate is fabricated by precisely machining a single large block of granite or the like. An extremely high shape accuracy is also required to the posts and beam, which make up the gantry section. Thus, in conventional gantry-type XY stages, the posts and beam of the gantry section are formed by polishing and processing castings of iron or iron alloy (hereinafter collectively called “iron casting”). This is because the gantry section formed of forging, for example, rolled steel would inevitably suffer from bowing in the rolling direction, thereby failing to ensure a sufficient shape accuracy. Also, the posts and beam, when formed of iron castings, can maintain a high shape accuracy because the iron has a Young's modulus of approximately 206 GPa and therefore a high rigidity, so that they can suppress deformations such as deflection due to their own weights, twisting associated with movements, and the like.
However, the aforementioned prior art technique has problems as shown below. Generally, for manufacturing TFT substrates for liquid crystal displays, multiple-chamfering is performed for simultaneously forming a plurality of TFT substrates on a single mother glass. Recently, there is a tendency of increasing the number of TFT substrates formed on a single mother glass for reducing the manufacturing cost of liquid displays. This drives mother glasses to become larger in size year by year, and associated with this, an increase in size is also under way in XY stages for use in laser repair apparatuses for liquid crystal displays. Consequently, the gantry section increases in mass, and moves over a longer distance.
As a result, when the gantry section is moved at high speeds, its moment of movement causes the granite plate of the base section to wobble, and the wobbles are transmitted to a laser processing unit attached to the gantry section. This causes wobbles in an image for observing a liquid crystal display to be repaired. Then, since the liquid crystal display cannot be processed for repair until the wobbles comes to end, causing a longer processing time per liquid crystal display. When the gantry section is moved at low speeds, the occurrence of wobbles can be limited, but the processing time per liquid crystal display will become longer after all.